1. Field of the Invention
The present invention relates to gate valves for controlling material flow along a flowpath. More particularly, the invention relates to an adjustable lockout device using one or more compression keys to securely lock the gate valve in a desired operating position.
2. Description of the Prior Art
Those ordinarily skilled in the art will appreciate that it is often necessary or desirable to securely lock a flow control or gate valve in a particular operating position, typically either fully open or fully closed. This is true, for example, where the valve or associated downstream components are being repaired such that a change in actuation or flow state could be damaging to the valve or components or injurious to a worker. Locking the valve in a particular position is commonly accomplished using a lockout device fitted to the gate valve.
A number of conventional valves are not designed to be locked out, and must therefore be retrofitted with structure for selectively locking the valve. Those ordinarily skilled in the art will appreciate that it is virtually impossible to precisely retrofit a valve such that it can be reliably and accurately locked in a fully open, fully closed, or other exact position. Even where the effects of component tolerances can be minimized, subsequent wearing can result in a significant amount of "play" or movement of the valve even when locked.
Existing lockout devices include mounting (e.g., welding) a locking element to the valve assembly, the element having a hole which is aligned with some part of the valve. A pin is then inserted into the hole and engages the valve to prevent movement thereof. Unfortunately, actuation forces applied to the valve translate into shearing forces on the pin. Thus, the ability of such a lockout device to prevent movement is limited to the shear strength of the pin, which is typically 66% to 70% of its yield.
Furthermore, a number of existing lockout devices are not tamperproof, and consequently may be removed by unauthorized personnel or workers having no knowledge that the valve should remain locked out.